1. Field of the Invention
The present invention relates to a video signal reproducing apparatus adapted for use in a video tape recorder (VTR) for playback of high-definition television signals or the like having a large amount of recording information.
2. Description of the Prior Art
Technical development is in progress with respect to a novel video transmission system termed high-definition television which is capable of displaying a video image with a high resolution. In such high-definition television system, where a video signal bandwidth is much wider than that in a standard transmission system based on the NTSC format or the like, it has been proposed to perform signal transmission through compression of the bandwidth by a specific method. One of the known methods for such bandwidth compression is termed MUSE (multiple sub-nyquist sampling encoding).
When a high-definition television signal is recorded by the use of a VTR or the like, the recording band can be narrowed by directly recording, without demodulation, the video signal band-compressed by the MUSE (hereinafter referred to as MUSE signal), so that an advantage is achievable in simplifying the constitution of a recording apparatus.
In a VTR for recording and reproducing such MUSE signal, there has been proposed a segment recording process which forms an image of one field by using a plurality of signal tracks. The MUSE signal has a narrower bandwidth but is approximately twice as wide as a conventional television signal based on the NTSC format and so forth. Therefore, when MUSE signals are recorded on a magnetic tape 101 as shown in FIG. 12 by means of two magnetic heads 100A and 100B which are mounted on a rotary head drum 100 with mutually different azimuths, there may be contrived an operation of, as shown in FIG. 13, first recording upper-half horizontal line signals of one field image on an azimuth-A track 102A by the magnetic head 100A having an azimuth A, and then recording lower-half horizontal line signals of one field image on an azimuth-B track 102B by the magnetic head 100B having an azimuth B.
According to such operation, each field is divided into two segments, with each segment recorded in two tracks. A segment recording operation records the upper half of one field on the track formed by the magnetic head 100A and records the lower half of one field on the track formed by the magnetic head 100B, hence increasing the available recording area per field to thereby compensate for the wide signal band.
It is customary in a VTR to provide a fast-forward playback mode or a rewind playback mode for moving a magnetic tape in a forward or reverse direction at a speed higher than a standard speed. In such fast-forward or rewind playback operation, however, noise bars are generated in a reproduced image since the magnetic heads 100A and 100B scan tracks recorded at mutually different azimuths.
The loci of the magnetic heads are oblique, as represented by thick lines in FIG. 14(a) if a double-speed playback operation is performed by the use of a magnetic head where azimuth-A tracks denoted by vertical frames A and azimuth-B tracks denoted by vertical frames B adjacent to the azimuth-A tracks are formed alternately. Shaded portions of the tracks can be reproduced when the azimuth-A magnetic head is scanning an azimuth-A track during its scan of a thick-frame locus HA and when the azimuth-B magnetic head is scanning an azimuth-B track during its scan of a thick-frame locus HB.
However, when the magnetic heads are scanning tracks formed with mutually different azimuths, the recorded signals are not reproduced at sufficiently high levels in the blank (unshaded) portions due to the difference between the head and track azimuths, hence causing noise bars in the reproduced image.
FIG. 14(a) illustrates a result of reproducing fields of a 2-channel 3-segment composition at a double speed; FIG. 14(b) illustrates a result of reproducing fields of a 2-channel 3-segment composition at a triple speed; FIG. 14(c) illustrates a result of reproducing fields of a 2-channel 2-segment composition at a double speed; and FIG. 14(d) illustrates a result of reproducing fields of a 2-channel 2-segment composition at a triple speed. It is found from such examples that the number of noise bars increases in accordance with an increase in the playback speed.
The above problem may be addressed by eliminating the portions of the signals with noise bars. However, in regard to the tracks formed with the same azimuth, noise bars appear at the same positions in the individual tracks as is obvious from the examples illustrated, so that the above method of eliminating the track portions with noise bars fails to accurately reproduce the signals of such portions, thereby deteriorating the quality of the reproduced image.